Electrode arrangement for electrochemical cells

ABSTRACT

Electrode arrangement for electrochemical cells. A deformable sandwich structure (working electrode, insulator, secondary electrode, insulator) forms a primary electrode arrangement. A three-dimensional structure can be formed by rolling up the primary sandwich structure around and axis. The shapes and material structures of electrodes and insulators co-operate with each other to enable axial and/or radial flow of an electrolyte which is pumped through the electrode roll. With such electrode rolls a high ratio of electrode surface to cell volume can be attained. Furthermore, by mounting one or more of the electrode rolls on a hollow axle and pumping the electrolyte through orifices of the axle from its interior into the electrode rolls, the scale-up of current and voltage of a cell is considerably facilitated and advantageously achieved.

BACKGROUND OF THE INVENTION

This invention relates to an electrode arrangement for electrochemicalcells.

A very important component of an electrochemical cell is the electrodearrangement contained in it. Since the electrochemical reactions takeplace at an electrode surface, a major design consideration is to obtaina high electrode area in as small a cell volume as is practicable.

Conventional cell designs have flat electrodes, made of whole sheets orplates, which are either taken in pairs (anode and cathode) or inmultiples as in the filter-press design. A disadvantage of thisconventional electrode design is the relatively low electrode area perunit cell volume. This limitation has been succesfully overcome withporous or particulate electrode (British Chemical Engineering, Vol. 16,No. 2/3, Feb./Mar., 1971, pp. 154-156, p. 159), but other difficultieshave been introduced. These include the difficulty to maintain anon-uniform potential and current density distribution within theelectrode system itself.

SUMMARY OF THE INVENTION

An object of the present invention is therefore to provide an electrodearrangement for electrochemical cells with which a high ratio ofelectrode area to cell volume and a uniform potential and currentdistribution within the electrode arrangement can be attained. Furtherobjects of the invention are to simplify cell construction and tominimise materials used so as to minimise cost.

According to this object the present invention provides an electrodearrangement for electrochemical cells comprising a sandwich arrangementof:

AT LEAST TWO ELECTRODES MADE FROM DEFORMABLE MATERIAL,

FIRST INSULATING MEANS FOR PREVENTING DIRECT ELECTRICAL CONTACT BETWEENTHE ELECTRODES, AND

SECOND INSULATING MEANS FOR PREVENTING DIRECT ELECTRICAL CONTACT BETWEENONE OF THE ELECTRODES AND OTHER ELECTRODES OR OTHER CONDUCTING PARTS OFTHE ELECTROCHEMICAL CELL,

THE SANDWICH ARRANGEMENT OF ELECTRODES AND INSULATING MEANS FORMING ADEFORMABLE ELECTRODE ARRANGEMENT, AND THE ELECTRODES AND THE INSULATINGMEANS HAVING SHAPES AND MATERIAL STRUCTURES WHICH CO-OPERATE WITH EACHOTHER TO ENABLE THE FLOW OF AN ELECTROLYTE THROUGH THE ELECTRODEARRANGEMENT.

In a preferred embodiment of the invention the sandwich arrangement isrolled up around a geometrical axis. This form given to the electrodearrangement enables to attain at the same time a high ratio of electrodesurface to cell volume and an homogeneous distribution of both currentand potential difference within the electrode arrangement.

A preferred use of the electrode arrangement according to the inventionis for oxidizing diaceton-L-sorbose to diaceton-L-ketogulonic acid.

The electrode arrangement according to the invention can also be usedfor making an electrochemical cell of high capacity, with which thefollowing technical aims can be attained:

a. very high admissable values of the operating voltage and/or current;

b. simple distribution of the electrolyte into the electrode system;

c. minimisation of the construction materials used;

d. simple design making possible mass-production of electrodearrangements and electrochemical cells.

This is achieved with an electrode arrangement comprising at least oneelectrode roll formed by rolling up the above sandwich electrodearrangement (provided by the instant invention) around a hollow axle,which has orifices at certain positions to enable the electrolyte toflow from the interior of the hollow axle into the electrode roll.

DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a schematic cross section of an electrode arrangementaccording to the invention,

FIG. 2 shows a schematic perspective view of a preferred form given tothe electrode arrangement of FIG. 1 for using it in an electrochemicalcell,

FIG. 3 shows a cross-section of a preferred embodiment of the electrodearrangement of FIG. 1,

FIG. 4 shows a schematic representation of some material structures thatcan be used for the electrodes (8, 9, 10, 11) and for the insulatingmaterials (8, 10, 11),

FIG. 5 shows a schematic top view of the electrode arrangement of FIG.1, wherein each electrode has a single electrical connnection (theinsulating materials are not shown),

FIG. 6 shows a schematic top view of the electrode arrangement of FIG.1, wherein each electrode has multiple electrical connections (theinsulating materials are not shown),

FIG. 7 shows a schematic representation of a cross-section of anelectrode arrangement with segmented electrodes for bipolar operation(prior to rolling up),

FIG. 8 shows a schematic cross-section view of an electrolyte cell whichcontains an electrode arrangement according to the invention.

FIG. 9 shows a schematic cross-section of a first embodiment of anelectrochemical cell which comprises several electrode rolls of the typeshown in FIG. 2,

FIG. 10 shows a perspective view of a preferred form of the axle of theelectrochemical cell shown in FIG. 9,

FIG. 11 shows a schematic representation of one form of electricalconnection of the electrochemical cell of FIG. 9,

FIG. 12 shows a schematic top view and a schematic cross-section of theelectrode arrangement (prior to rolling it) which is used in a secondembodiment of an electrochemical cell,

FIG. 13 shows a perspective view of an electrode roll made by rolling upthe electrode arrangement of FIG. 12,

FIG. 14 shows a schematic cross-section of the electrode roll of FIG.13,

FIG. 15 shows a schematic cross-section of the bipolar electrodearrangement which is used in a third embodiment of an electrochemicalcell,

FIG. 16 shows a schematic cross-section which illustrates in detail thestructure of the electrode arrangement of FIG. 15,

FIGS. 17a, 17b show a top view of the electrode strips employed formaking the electrode arrangement shown in FIGS. 15 and 16. The electrodestrip of FIG. 17a is also employed for making be electrode arrangementshown in FIGS. 12, 13, 14.

DESCRIPTION OF THE PREFERRED EMBODIMENT

As schematically shown in FIG. 1, an electrode arrangement 5 accordingto the invention comprises a sandwich arrangement of at least twoelectrodes 1, 2 made from deformable material, first insulating means 3which prevent a direct electrical contact between the electrodes, andsecond insulating means 4 which prevent direct electrical contactbetween one of the electrodes and other electrodes or other conductingparts (e.g. a cell-container) of the electrochemical cell wherein theelectrode arrangement is incorporated.

The materials for the electrodes 1, 2 and the insulating means 3, 4 arechosen in order to make a deformable electrode arrangement 5. Thematerials for the electrodes and the insulating means have shapes andmaterial structures which co-operate with each other to enable the flowof an electrolyte through the electrode arrangement.

For using the electrode arrangement according to the invention in anelectrochemical cell, it is convenient to give the electrode arrangementa form enabling to get a maximum ratio of electrode surface to cellvolume. This design criterion is satisfied by the electrode roll 6 shownin FIG. 2, which is formed by rolling up the electrode arrangement shownin FIG. 1 around a geometrical axis A-A'.

In the drawings, the electrodes are shown to be rather loosely wound.Although this could be the case in certain applications, e.g. when thereis considerable gas evolution from one or more electrodes, for mostpurposes the electrodes 1,2 and insulating layers 3,4 are normally woundtightly around a central core 30 (FIG. 5,6) to obtain as high anelectrode surface area within the fixed volume of the cell as isrequired.

The electrode roll 6 is preferably contained in a vessel (not shown inFIG. 2) which has the necessary inputs and outputs and which is suitablyof cylindrical construction.

As shown in FIG. 3, the insulating means 3,4 separating the electrodes1,2 in FIG. 2 must serve several purposes. The first one is toelectrically insulate electrodes at different potentials from eachother. The second one is to co-operate with the electrodes 1,2 to formcavities 7 to enable the flow of an electrolyte through the electrodearrangement. An additional function of the insulating means can be toseparate solutions around different electrodes.

The material for the insulating means can be any chemically inertsubstance which has a suitable form and material structure. As shown inFIG. 4, the insulating means can be made, e.g. from porous 8 orperforated sheets 10, woven synthetic materials or woven glass fibre 11.The insulating means can also be made from an ion-exchange membrane.

As stated above, besides preventing direct electrical contact betweenelectrodes at different potentials, a second function of the insulatingmeans is to co-operate in providing cavities 7 within the electrodearrangement. These two functions can be achieved with separatecomponents, in which case any of the aforementioned materials for use asan insulator can also be used for forming the cavities 7 between theelectrodes. On the other hand, specifically constructed singlematerials, e.g. rippled sheets 43,44, as shown in FIG. 3 or wovenmaterials 11, can be used for performing both functions.

The materials for the construction of the electrodes should have goodelectrical conductivity, suitable electrochemical properties and goodcorrosion properties, which satisfy the requirements of the particularapplication. Most metals are suitable e.g. platinum, gold, palladium,copper, nickel, lead, tin, cadmium or any other suitable metal or alloythereof. Non-metalic materials can also be used. For instance, carbonwhich is in a flexible form, e.g. a deposit on an electricallyconducting substrate, carbon filaments woven filaments, or felts, can beused. The electrode may also have special coatings, e.g. oxidisedruthenium or lead dioxide or oxidised nickel hydroxide. As representedin FIG. 4, the electrode rolls can be constructed from sheet materials,perforated sheets 10 or gauzes 11.

The vessel holding the electrode roll can be constructed from anychemically inert material (inert to the electrolyte and under theoperating conditions employed), that has a suitable mechanical strength.

An electrolyte, which can be a solution or a pure liquid or a mixture oremulsion of solutions or liquids or both, is the feed-stock for theelectrolytic cell described hereinafter.

During operation of the cell, the electrolyte must be made to enter thecavities 7 between the electrodes. This flooding of the cavities may beachieved by running the electrolyte into the electrode-roll in either oftwo main directions or a combination of these two. The first maindirection along which an electrolyte can be fed into the roll isaxially, i.e. along the direction of the axis A-A' of the roll. In thiscase, it is necessary to seal (electrolyte impermeable) the outside ofthe electrode roll to the inside wall of the container. This is to forcethe electrolyte to flow through the electrode roll and not around theoutside. The second main direction to feed an electrolyte into the rollis radially either inwards or outwards from the central core 30 (FIGS.5,6). In this second case the central core of the roll has to be hollowor to provide some other form of pathway for the electrolyte to enter orbe removed from the centre. In addition the electrode materials and theinsulating means must be electrolyte permeable. As schematicallyrepresented in FIG. 4, they could either be porous 8, perforated sheets10 or gauzes 11.

Electrical energy can be supplied to the electrode roll 6 (FIG. 2) bymeans of simple and suitable connections. In the following some forms ofelectrical connection are described.

FIG. 5 shows a shematic top view of an electrode roll with twoelectrodes. Point 12 represents the electrical connection of theelectrode and the axle 30. Point 13 represents the connection of thesecond electrode 2 and the cell container. Electrical power is fed tothe electrode roll via the axle 30 and the cell container. This form ofelectrical connection is suitable, when the voltage drop over the wholelength of the rolled electrodes is negligible for the electrochemicalprocess being performed.

FIG. 6 shows a second form of electrical connection with which theelectrical power is fed to each electrode at several positions alongtheir length by making power connections to the edges of the coiledelectrodes, e.g. at points 14, 15, 16 and, respectively, 17, 18, 19.This second form of electrical connection is suitable for relativelyhigh current inputs, in which case the potential drop along theelectrode lengths may be prohibitively high.

A third way of feeding electrical power to the electrodes can beachieved with an electrode arrangement for bipolar operation. FIG. 7shows a schematic cross-section of an electrode arrangement for bipolaroperation, prior to rolling it around an axle 30. The electrode layers20, 21 are formed of conducting segments which are electricallyinsulated from each other. Each segment 26 of one electrode layer 21overlaps two halves of adjacent segments 22, 23 of the other electrodelayer 20. In bipolar operation, the electrical power is fed by applyingthe operating voltage between the end segments 27, 28 of the electrodearrangement. As with all bipolar electrode arrangements the totalcurrent flowing through the electrode arrangement is the same as for abipolar arrangement with only one pair of electrodes, while theoperating voltage is equal to the potential difference between a workingelectrode segment and its corresponding secondary electrode segmenttimes the number of such electrode segment pairs, i.e. working andsecondary electrode segments.

To achieve efficient bipolar operation it is necessary to employ aninsulating separator 24 that enables ionic conduction (solutionpermeable) between the electrode layers 20 and 21 and an insulatingseparator 25 that prevents both ionic and electronic conduction betweendifferent pairs of electrode layers. This is of importance when thesandwich shown in FIG. 7 is rolled up around the axis 30. When only apair of electrode layers is used, separator 25 serves to isolate thispair from undesirable electric contacts, e.g. from the cell container.

The use of an electrode arrangement according to the invention isdescribed with reference to FIG. 8, which shows a cross-section of anelectrolytical cell along its central axis. The electrode arrangement 32comprises one anode and one cathode. Each electrode is a nickel sheet3000 × 150 × 0.1 mm. The separator between the electrodes is made of asynthetic cloth. The core of the coiled electrode arrangement is a solidnickel rod 31. The electrode sandwich 32: nickel foil, separator, nickelfoil, separator is rolled up tightly around the nickel rod 31. Theelectrode roll 31, 32 is lodged in a cell container, which comprises astainless cylinder 34, an upper PVC cover 35 that lodges the upper endof the nickel rod 31 and a perforated PVC disc 36, which is screwed tothe lower end of the nickel rod. The nickel rod 31 makes electricalcontact with the anode sheet of the roll is provided with a connectionbolt 37 to serve as current feeder to the anode. The cathode sheet ofthe roll makes a tight press fit with cylinder 34, which is providedwith a connection bolt 38 to serve as current feeder to the cathode. Thediameter of the central nickel rod 31 is 22 mm and the inside diameterof the container 60 mm. In operation the electrolyte is pumped into thecell at an inlet 39 at the bottom of the container and through the roll32 in a direction parallel to the axis of the nickel rod 31. Theelectrolyte leaves the cell at an outlet 40 near the top of the cellcontainer.

Three examples of the electrolyte processes, e.g. electrochemicaloxidations, that can be performed with the cell described above aregiven below:

Oxidation of ethylamine to acetonitrile:

A solution 0.85 M in ethylamine and 1 M in potassium hydroxide is pumpedcontinuously through the cell. Electricity is applied to the cell andthe current density is adjusted at 2,33 mA/cm² (the electrode area isabout 9000 cm²). The cell voltage during the electrolysis lies in therange of 1.8 to 2.0 Volt. After 4 hours the electrolysis is stopped andthe material yield of acetonitrile lies about 67.8%.

Oxidation of benzyl alcohol to benzoic acid:

The electrolysis solution (emulsion) is 0.5 mole benzyl alcohol, 1.0mole potassium hydroxide and 5 g sebacic acid in 500 ml water. Thesebacic acid is added to obtain an emulsion of the immiscible benzylalcohol in water. This solution is pumped continuously through the celland a current of 10 Amperes is applied to the cell for 260 minutes. Thesolution is then adjusted to pH = 1 and a precipitate of benzoic acidcontaining some sebacic acid is obtained. The weight of the driedprecipitate lies about 25.8 g. Pure benzoic acid is obtained bydistillation of the crude product. The yield lies about 8.0 g.

The nickel electrodes of the electrolytic cell described above can bepre-treated by electrodeposition of a layer of nickel oxide. This can bedone as follows. An aqueous solution: 0.1 M nickel sulphate, 0.1 Msodium acetate and 0.005 M sodium hydroxide is pumped through the cellcontinuously. A current of 50 Amperes is applied to the cell for 5seconds, the polarity of the supply is then reversed and 50 Ampere ofthe opposite polarity are applied to the cell for 5 seconds. Thisprocedure is repeated 5 times.

The cell with pre-treated electrodes as described above can be used tooxidize diacetone-L-sorbose (DAS) to diacetone-L-ketogulonic acid (DAG).For this, 500 ml of a 30% solution of DAS and 2 M potassium hydroxide ispumped through the cell continuously while a current of 50 Amperes isapplied. The electrolysis is continued until significant amounts ofoxygen evolve from the anode. The solution is then cooled to 0° C. andbrought slowly to pH = 1. DAG precipitates out. It is filtered off,dried an weighed. A 95% material yield is obtained.

The advantages of an electrode arrangement according to the inventionare as follows:

The sandwich structure of the electrode arrangement 5 (FIG. 1) enablesuse of very thin and even delicate electrode materials.

Three-dimensional electrode arrangements like the electrode roll 6 canbe made from the basic electrode arrangement 5 depicted in FIG. 1. Inthis way a mechanically rigid and self-supporting electrode arrangementis made from a deformable one. Such compact electrode rolls enablereaching a high ratio of electrode surface to cell volume, when theelectrode roll is placed in a suitable cell-container.

When the electrolyte flows axially through the electrode roll, theunusual ratio of path width (the length of the electrodes) to pathlength (the width of the electrodes) enables to minimise the electrolyteresidence time within the cell.

With the electrode arrangement 5 according to the invention, it ispossible to make very small inter-electrode gaps. This enables tominimising the volume of inactive electrolyte and the correspondingpower losses. Convection conditions at the electrodes can also beimproved by use of small interelectrode gaps, provided gas is developedat least at one electrode.

An important advantage of the electrode arrangement according to theinvention is that uniform mass transport conditions are obtained asfollows: The flow of electrolyte through the separator layers 3, 4 canbe employed to introduce turbulence into the electrolyte stream. Theturbulence given to the electrolyte flow in passing through e.g. a wovencloth separator maintains uniform mass transport conditions over thewhole electrode surface.

Furthermore, the electrode arrangement 5 according to the inventionmakes it possible to supply electrical power to the electrodes in such away that a very uniform distribution of current and potential differencecan be attained within the electrode arrangement.

Use of an electrode arrangement according to the invention is by nomeans limited to electroorganic processes, but extends to a plurality ofother electrochemical processes.

As already mentioned above scale-up of the current with the simpleelectrode roll of the cell shown in FIG. 8 is limited by potential dropsalong the electrodes.

In the following, three preferred embodiments of electrode arrangementsaccording to the invention are described, with which inter alia theabove scale-up limitation can be overcome.

Embodiment 1 FIGS. 9, 10, 11):

FIG. 9 shows an electrochemcial cell comprising a number of electroderolls 43 arranged on an axle 51. FIG. 9 shows a cell with 10 electroderolls. This number is just an example. However, an even number willusually be employed. The main features of this embodiment are asfollows:

The axle of the cell is hollow, e.g. a pipe. The electrode rolls 43 areof the type described above with reference to FIG. 2. The electroderolls are arranged in pairs 52 with a gap 53 between them. In operation,the electrolyte is fed into the gap 53 of each pair of electrode rollsthrough orifices 54 of the axle 51. The gap 53 is wide enough to enableconvenient flow of electrolyte between the electrode rolls forming apair. The electrolyte is prevented from exiting directly into the space55 surrounding the core of the cell by a leak-proof metallic band 56which joins together the electrode rolls forming a pair. The electrolyteis thus forced to flow through each pair 52 of electrode rolls, that is,through the cavities 7 (see FIG. 3) within the electrode arrangement.After flowing through the electrode rolls, the electrolyte exits fromthe cell by running through gaps 57 between adjacent pairs of electroderolls into the space 55 surrounding the core of cell and out by anoutlet 58. Electrical connection to the row of electrode rolls can beeither parallel or series. In FIG. 9 the series connection is shown.Power is fed to the two end rolls 41, 43 only in one case theelectricity being fed to the anode and in the other case to the cathode.The electricity is fed from the power source through bus-bars 59, 60 toisolated metal sections 61, 62 of the axle 51, which act as currentfeeders to the two end rolls. The rolls which form a pair areelectrically connected together by the metallic bands 56, and the rollsof different pairs are connected by isolated conduction sections 63 ofthe axle. FIG. 11 shows the parallel electrical connection of theelectrode rolls. In this case, the axle 51 comprises a continuouselectrical conductor 50 which makes electrical connection with oneelectrode of each roll and the metal bands 56 act as the current feedersto the other electrodes.

The materials and construction of each roll are as described previouslyand illustrated by FIGS. 1, 2, 3, 4. The use of a bipolar arrangement asshown in FIG. 7 is also possible.

With this first embodiment, the above design aims (a-d) when making anelectrochemical cell can be achieved as follows:

Aim (a) is achieved by the use of several electrode rolls. Aim (b) isachieved by the use of a hollow axle with orifices to distribute theelectrolyte into the rolls. Aim (c) is achieved by eliminating the needto have a tight fitting metal container for the rolls. Aim (d) isachieved by constructing a large capacity cell from many small units ofthe same type.

Embodiment 2 (FIGS. 12, 13, 14, 17a):

Referring to FIG. 14 it can be noticed that like in Embodiment 1, theelectrolyte is introduced in the electrode roll 44 of the cell throughorifices 54 of the axle 51. The electrode arrangement used for thisEmbodiment is shown in FIG. 12. It comprises 6 elements: a cathode 70and an anode 71 both using an electrode material with perforations 72 atone side; two insulating means 3, 4 and two end sealing strips 73, 74.The end sealing strips are constructed from an electrically conductingmaterial (e.g. metal). A sealing compound or aid 75 can also be used toimprove the seal. The necessary overlapping of the layers is shown inFIG. 12 which includes both a top view and a cross-section of theelectrode arrangement prior to rolling it. FIG. 13 shows the electrodearrangement of FIG. 12 being rolled up around the axle 51. The metalstrips 73, 74 are of a suitable thickness so that the ends of the rollare solid with no possibility of a leak of electrolyte from within theroll. As shown in FIG. 14, the electrolyte is pumped into the rollthrough the holes 54 in the axis and the perforations 72 of one of theelectrode sheets. The electrolyte is prevented from exiting directlyfrom the cell by closing off the path provided through the perforations72 at the surface of the electrode roll with some leak-proof seal 76.The electrolyte flow path 77 goes through the roll to the other endwhere it is free to exit through the perforations 72 of the otherelectrode.

The electrical connection to the electrode roll is made by mounting thebus-bars directly onto the ends of the electrode roll as in 78, 79.These provide connection to the complete longitudinal edge of eachelectrode. This enables an almost limitless scale-up of the length ofthe electrodes and of the diameter of the electrode roll.

The materials for making the electrode roll of FIG. 13 are as follows:

The materials for the insulating means 3, 4 are as described previously.The electrodes are sheet form using materials as described above. Animportant difference however is the introduction of a row ofperforations 72 along one side and over the whole length of eachelectrode. The perforations 72 of the electrode sheets act as openingsfor distributing the electrolyte from the hollow axis into the electroderoll. The perforations 72 of one electrode serve as inlets and theperforations 72 of the other electrode as outlets. The position of theelectrode roll on the axle 51 enables an easy flow of the electrolytethrough the orifices 54 of the axle and through the inlet perforations72.

A sealing strip 73, 74 is incorporated in the electrode arrangement atboth sides. It must be constructed from an electrically conductingmaterial that does not corrode and is electrolyte impermeable. Thesealing strip is about the thickness of two layers of insulatingmaterial plus one layer of electrode material. The sealing strip acts asa means of conducting the electricity across the ends of the roll makingcontact with the whole side of one particular electrode and as a meansof stopping axial electrolyte flow out through the ends of the roll.

With this second embodiment, the above design aims (a-d) when making anelectrochemical cell are achieved as follows:

Aim (a) is achieved by the form of power feeding employed, which enablesuse of electrodes of almost unlimited length for making the electroderoll, that is, the diameter of the roll can also be scaled-up, almost atwill. This makes possible an almost limitless scale-up of the reactorcurrent with a single electrode roll, rather than with a plurality ofthem, as in Embodiment 1. Aim (b) is achieved through the use of ahollow axis with perforations and perforated electrode sheets. Aim (c)is achieved since the bulk of the construction materials are theelectrodes themselves. Aim (d) is achieved by the use of simple windingequipment for making the cell.

Embodiment 3 (FIGS. 15, 16, 17a, 17b):

This is a modification of Embodiment 2, wherein the main features ofEmbodiment 2 are retained, but in addition the electrode arrangementused is a much broader one and incorporates several bipolar electrodesheets placed side by side so as to enable scale up of the cell voltageas well as of the current. This third Embodiment achieves the designaims as Embodiment 2 and in addition makes possible scale-up of cellvoltage also [Aim (a)].

Referring to FIG. 15, it can be seen that like in Embodiments 1 and 2the axle 51 of the cell is hollow. The electrolyte is pumped in anelectrode roll 45 through perforations 54 of the axle 51 and throughperforations (72, 87) of the electrodes. The electrode arrangement usedfor this embodiment is illustrated by FIGS. 15 and 16. The electroderoll 45 has four layers, which are rolled up around the axle 51, theposition of which is indicated by line 86 in FIG. 16. The insulatingmeans 3, 4 are as described previously. One of the electrode layers 84is constructed from N electrode sheets 82 placed side by side withuniform spaces 90 between them and two end electrode sheets 81. Theother electrode layer 85 consists of N+1 electrode sheets 82, which arealso placed side by side with uniform spaces 90 between them. The sheetsof one electrode layer are placed so as to overlap two halves ofadjacent sheets of the other layer. This overlap is shown in FIG. 16 andis necessary for the bipolar operation of each electrode sheet. As shownby FIGS. 16 and 17a, 17b, the end electrode sheets 81 of the widestelectrode layer 84 have slots 72 along one side so as to allow thecirculation of electrolyte. The other sheets 82 of the electrode layer84 are broader (about 2 times the width of 81) and have perforations 87down their centre area and over their whole length. As shown by FIG. 15,the perforations 72, 87 of the sheets of the wider electrode layer 84lie facing the orifices 54 along the axis 51. This enables flow of theelectrolyte through path 88. The electrolyte exits through outlets 89.Each outlet 89 lies in front of a perforation 87 of the other electrodelayer 85. As in Embodiment 2, a sealing and electrically conductingstrip 73, 74 completes the electrode arrangement at each end.

The electrical connections to the electrode roll 45 are similar to theones of Embodiment 2, the electricity being fed directly only to theside-most electrode sheets. The other sheets acting in a bipolar fashiontransfer the electricity through the electrode arrangement.

The materials for making the electrode arrangement of this thirdembodiment are similar to the ones described for Embodiment 2, but theelectrode sheets for bipolar operation differ from the ones previouslydescribed in that the perforations would normally be down the centrearea of the electrode and distributed along its complete length.

A common feature of all three Embodiments described above is the use ofa hollow axis 51 with perforations 54 for feeding the electrolyte intothe electrode roll(s). As the axle should not short-circuit electrodeswith different potentials, the axle has either to be made ofnon-conducting material or to have a structure which prevents suchshort-circuits. The axle 51 can also be constructed in a concentricfashion with the outermost tubes acting as current feeders for theelectrodes. Current feeders at different potentials have of course to beelectrically insulated from each other. As the axle 51 acts in additionas a means of support for the electrode rolls, it will normally beconstructed from materials that are strong enough to support the rollsand also a corrosion resistant material.

It should be clear that among other electrochemical processes, theelectrolytical oxidations mentioned above to exemplify use of cellaccording to FIG. 8 can also be performed with the above Embodiments 1-3of an electrochemical cell according to the invention.

I claim:
 1. An electrode arrangement for electrochemical cells includingat least one electrode roll formed by spiralling a deformable sandwicharrangement of electrode layers and spacing layers for preventing directelectrical contact between them, at least one of the spacing layersbeing ion-permeable and the electrodes and spacing layers having shapesand material structures which co-operate with each other to enableelectrolyte flow through the electrode roll, the electrode arrangementbeing characterized in that the electrode rolls are rolled up around ahollow axle and arranged by pairs, each pair having a gap between theelectrode rolls and the hollow axle having orifices which enableelectrolyte flow from the interior of the hollow axle into the gap ofeach pair of electrode rolls.
 2. An electrode arrangement according toclaim 1 further comprising a leak-proof band around each pair ofelectrode rolls, for closing the gap between the electrode rolls,whereby the whole of the electrolyte flowing into the gap is forced toflow through the electrode rolls.
 3. An electrode arrangement forelectrochemical cells including at least one electrode roll formed byspiralling a deformable sandwich arrangement of electrode layers andspacing layers for preventing direct electrical contact between them, atleast one of the spacing layers being ion-permeable and the electrodesand spacing layers having shapes and material structures whichco-operate with each other to enable electrolyte flow through theelectrode roll, the electrode arrangement being characterized in thatthe electrode roll is rolled up around a hollow axle, the hollow axleand the electrodes having each orifices at specified positions, whichorifices co-operate with each other for enabling electrolyte flow fromthe interior of the hollow axle into the electrode roll, the position ofthe orifices being so specified that the electrolyte flows first in adirection perpendicular to the axle and then parallel thereto.
 4. Anelectrolyte arrangement for electrochemical cells according to claim 3wherein the electrode roll includes at least one pair of electrodelayers for bipolar operation, each of which is composed of a pluralityof perforated electrode strips, which are rolled around the axle inspaced relationship, each strip of one electrode layer overlappingapproximately two halves of adjacent strips of the other electrodelayer.
 5. An electrode arrangement for electrochemical cells includingat least one electrode roll formed by spiralling a deformable sandwicharrangement of electrode layers and spacing layers for preventing directelectrical contact between them, at least one of the spacing layersbeing ion-permeable and the electrodes and spacing layers having shapesand material structures which co-operate with each other to enableelectrolyte flow hrough the electrode roll, the electrode arrangementbeing characterized in that for enabling electrical power feed throughthe axial ends of the electrode roll each longitudinal side of thesandwich arrangement includes a strip-shaped layer of electricallyconducting material which overlaps and is in direct electrical contactwith one longitudinal edge of one electrode, so that the electrodestructure formed by rolling the sandwich arrangement has conductingends, each end enabling to feed electrical current to the whole lengthof one electrode layer.
 6. An electrode arrangement according to claim5, wherein the electrically conducting strip-layers are placed on thelongitudinal edges of the electrode layers prior to rolling and arerolled with the electrode arrangement for sealing both ends of theelectrode roll in axial direction.
 7. An electrode arrangement forelectrochemical cells including at least one electrode roll formed byspiralling a deformable sandwich arrangement of electrode layers andspacing layers for preventing direct electrical contact between them, atleast one of the spacing layers being ion-permeable and the electrodesand spacing layers having shapes and material structures whichco-operate with each other to enable electrolyte flow through theelectrode roll, the electrode arrangement being characterized in thatthe electrode layers are longitudinally segmented for bipolar operation,each electrode segment of one of the electrode layers overlappingapproximately two halves of adjacent segments of the other electrodelayer and the end segments of one of the electrode layers having each aterminal for electrical connection; and the insulating means betweenelectrodes that form a pair for bipolar operation enable ionicconduction, whereas the insulating means between different electrodepairs, that is, electrode pairs other than the pair designed to operatetogether, prevent both ionic and electronic conduction betweenelectrodes of such different pairs.
 8. An electrode arrangement forelectrochemical cells, comprising a sandwich arrangement of at least twoelectrodes made from deformable material, wherein the electrodes arelongitudinally segmented for bipolar operation, each electrode segmentof one of the electrode layers overlapping approximately two halves ofadjacent segments of the other electrode layer and the end segments ofone of the electrode layers having each a terminal for electricalconnection, first insulating means for preventing direct electricalcontact between the electrodes, second insulating means for preventingdirect electrical contact between one of the electrodes and otherelectrodes or other conducting parts of the electrochemical cell, theinsulating means between electrodes that form a pair for bipolaroperation enabling ionic conduction, whereas the insulating meansbetween different electrode pairs, that is, electrode pairs other thanthe pair designed to operate together, prevent both ionic and electronicconduction between electrodes of such different pairs, the sandwicharrangement of electrodes and insulating means forming a deformableelectrode arrangement, and the electrodes and the insulating meanshaving shapes and material structures which co-operate with each otherto enable the flow of an electrolyte through the electrode arrangement.9. An electrode arrangement for electrochemical cells, comprising asandwich arrangement of at least two electrodes made from deformablematerial, first insulating means for preventing direct electricalcontact between the electrodes and second insulating means forpreventing direct electrical contact between one of the electrodes andother electrodes or other conducting parts of the electrochemical cell,said sandwich arrangement being rolled up around a geometrical axis toform an electrode roll, at least one of said electrode rolls beingrolled up around a hollow axle, said electrode roll further comprisingelectrically conducting sealing strips placed on one longitudinal edgeof each electrode prior to rolling and rolled with the electrodearrangement for sealing both ends of the electrode roll in axialdirection, the electrodes of said electrode roll having perforations andsaid hollow axle having orifices at certain positions whereby to enablethe electrolyte to flow from the interior of the hollow axle through theorifices of the hollow axle into the electrode roll in a directionperpendicular to the axle, said sandwich arrangement of electrodes andinsulating means forming a deformable electrode arrangement, and theelectrodes and the insulating means, as aforesaid, having shapes andmaterial structures which co-operate with each other to enable the flowof an electrolyte through the electrode arrangement.
 10. An electrodearrangement for electrochemical cells, comprising a sandwich arrangementof at least two electrodes made from deformable material, firstinsulating means for preventing direct electrical contact between theelectrodes and second insulating means for preventing direct electricalcontact between one of the electrodes and other electrodes or otherconducting parts of the electrochemical cell, said sandwich arrangementbeing rolled up around a geometrical axis to form an electrode roll, atleast one of said electrode rolls being rolled up around a hollow axle,the electrode roll including at least one pair of electrode layers forbipolar operation, each of which is composed of a plurality ofperforated electrode strips, which are rolled around the axle in spacedrelationship, each strip of one electrode layer overlappingapproximately two halves of adjacent strips of the other electrodelayer, said electrode roll having perforations and said hollow axlehaving orifices at certain positions whereby to enable the electrolyteto flow from the interior of the hollow axle through the orifices of thehollow axle into the electrode roll in a direction perpendicular to theaxle, said sandwich arrangement of electrodes and insulating meansforming a deformable electrode arrangement, and the electrodes and theinsulating means, as aforesaid, having shapes and material structureswhich co-operate with each other to enable the flow of an electrolytethrough the electrode arrangement.